EDUCATION: The Really Big Chill

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Science  03 Mar 2006:
Vol. 311, Issue 5765, pp. 1221e
DOI: 10.1126/science.311.5765.1221e

If the “snowball Earth” hypothesis is right, our planet froze at least three times in the distant past. To learn more about the controversial notion, schuss over to this site sponsored by geologist and snowball Earth advocate Paul Hoffman of Harvard University. The hypothesis holds that ice encased the planet for several million years starting about 2.2 billion years ago, again 710 million years ago, and then 640 million years ago. Background pages present supporting evidence and probe the cold spells' possible causes and consequences for life. One trigger may have been the continents clumping along the equator, where the torrid conditions could have paradoxically set off a global chilling by accelerating a form of weathering that depletes atmospheric carbon dioxide. The site also offers nearly 200 downloadable slides for classroom use, such as a map of “oases” where life might have endured the big freezes, and other resources.

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